Question: Vera is using her phone. Its battery life is down to $\dfrac25$, and it drains another $\dfrac19$ every hour. How many hours will her battery last?
Answer: We can think about this problem like this: $ {\text{number of hours}} = \dfrac{{\text{remaining battery life}}} {{\text{amount used per hour}}}$ ${\text{?}} = {\dfrac25} \div {\dfrac19}$ $\begin{aligned} {\dfrac25} \div {\dfrac19}&={\dfrac25}\times\dfrac91 \\\\ &=\dfrac{2\times9}{5\times1} \\\\ &=\dfrac{18}{5} \end{aligned}$ Her battery will last $\dfrac{18}{5}$ hours.